The present invention generally relates to the incubation of living cells and, more particularly, to a method and apparatus for the continued incubation of the cells in a liquid culture medium.
Incubation of cells in a liquid culture medium containing various nutrients has long been practiced. The cells in the culture medium consume the nutrients for the multiplication or the growth thereof, and the pH value of the culture medium naturally varies with progressive consumption of the nutrients and metabolism of the cells. When the nutrients are consumed to less than a certain concentration, or when the pH value of the culture medium varies to such an extent as to deviate from a pH range suited or required for the growth of the cells, the cells will no longer be active to increase, i.e., multiplicate or grow. Once such a condition has arisen, the continued, positive incubation of the cells is possible provided that the liquid culture medium in which the cells have been placed is replaced with a fresh one of the same composition.
Hitherto, the time at which the liquid culture medium should be replaced is determined by monitoring the liquid culture medium to see if the color of a pH indicator such as, for example, Phenol red, contained in the culture medium has changed as a result of the change in pH value. Once the time has been determined, a tray carrying the culture medium to be replaced is transported to a sterile room where the replacement takes place subsequently. During the transportation and the subsequent replacement, human labors intervene frequently, thereby posing such a problem that the culture medium may be often contaminated with foreign germs.
In any event, according to the conventionally practiced method, the determination of the pH value of the culture medium based on the change in color of the pH indicator does not necessarily bring about an accurate measurement, and it happens very often that the composition of the culture medium remains in a range unsuitable for incubation of the cells, or the culture medium is left for a long time under conditions unsuitable for incubation of the cell. In the worst case, the cells will be killed.
The killing of the cells may occur even when the culture medium has been contaminated with foreign germs as discussed above. This is because the pH value of the liquid culture medium may change with either metabolism of the contaminant germs or extraordinary multiplication of the contaminant germs.